Of GREATEST ATTRACTION, 225 



roid becomes oblong, and the attraction at the poles again di- 

 minifhes. This we may fafely conclude from the law of con- 

 tinuity, though the oblong fpheroid has not been immediately 

 confidered. 



XVIII. 



To find the force with which a particle of matter is attracted 

 by a parallelepiped, in a direction perpendicular to any of its 

 fides. 



First, let EM (Fig. 11.), be a parallelepiped, having the 

 thicknefs CE indefinitely fmall, A, a particle fituated anywhere 

 without it, and AB a perpendicular to the plane CDMN. The 

 attraction in the direction AB is to be determined. 



Let the folid EM be divided into columns perpendicular to 

 the plane NE, having indefinitely fmall rectangular bafes, and 

 let CG be one of thofe columns. 



If the angle CAB, the azimuth of this column relatively to 



AB, be called z, CAD, its angle of elevation from A, e, and m\ 



the area of the little rectangle CF > then, as has been already 



fhewn, the attraction of the column CG, in the direction AC, is 



_ 7, 



— . fin e $ and that fame attraction, reduced to the direction 

 AC 



AB, is -— . . fin e . cof z. This is the element of the attraction 

 AC 



• n? 

 of the folid, and if we call that attraction/, /= — — . fin e . cof z« 



AC ■ 



Now, If AB = a 9 becaufe 1 : cof z : : AC : AB, AC - = —£- r 



cof z 



2 



m 



fo that / == — . fin e » cof 2V 



J a 



But 



